Add meta/import_all.py for testing
Add meta/import_all.py for testing

Importing a module gives us a cheap way to implement some static tests.
Add a utility that can import all the modules in a package.

Test Plan:
Make sure it detects some errors

$ ./meta/import_all.py py/mel
.. ok ..
.. introduce an import to a module that doesn't exit ..
.. fails ..

Make sure it tests all the modules

$ ./meta/import_all.py py/mel --verbose
.. listing of tested modules looks correct ..

aevri/mel,aevri/mel